This application is based upon and claims the benefit of Japanese Patent Application No. 11-203568 filed on Jul. 16, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a pressure detection apparatus including two cases, which are fixedly assembled to form a pressure detection chamber, and to a method of manufacturing the same.
2. Description of the Related Art
JP-A-7-243926 proposes a pressure detection apparatus shown in FIG. 9. The pressure detection apparatus has a connector housing J1 as a first housing, and a main housing J2 as a second housing. The connector housing J1 and the main housing J2 are fixedly assembled to form a closed pressure detection chamber J3. An internal pressure of the pressure detection chamber J3 is detected by a pressure sensitive element J4, and is output as a sensor output voltage through a connector pin J5 that is electrically connected to the pressure sensitive element J4.
The two housings J1 and J2 are fixed together by caulking an opening edge portion J2a of the main housing J2 from a position indicated by a two dotted line onto the connector housing J1. Accordingly, the pressure detection chamber J3 sealed by an O-shaped ring J6 is provided. The pressure detection chamber J3 is filled with oil as a pressure transmittance medium.
In the conventional manufacturing method of the pressure detection apparatus as described above, however, it is difficult to crush the O-shaped ring J6 uniformly due to variations in caulking load when the two housings J1 and J2 are caulked, resulting in variations in volume of the pressure detection chamber J3. Because of this, the internal pressure of the pressure detection chamber J3 varies to cause variations in sensor output voltage (for instance, in a range of 30 mV to 40 mV) with respect to a target value. The variations in sensor output voltage appear as variations in output offset, thereby inhibiting improvement of output sensitivity. These adverse effects are especially prominent when a detecting pressure range is low and the sensor output voltage is small.
The present invention has been made in view of the above problem. A first object of the present invention is to provide a method for manufacturing a pressure detection apparatus by fixing a first case and a second case to decease variations in volume of a pressure detection chamber. A second object of the present invention is to provide a pressure detection apparatus having a structure, which can be manufactured without producing variations in volume of a pressure detection chamber.
According to a first aspect of the present invention, a pressure detection apparatus is manufactured by assembling a first case and a second case to form a pressure detection chamber closed therebetween and to form a space between an outer surface of the first case and an inner surface of the second case, and by filling the space with adhesive made of resin.
According to a second aspect of the present invention, a pressure detection apparatus has a first case, a second case connected to the first case to form a pressure detection chamber, and to define a space between an outer surface of the first case and an inner surface of the second case, and an adhesive filling the space. Accordingly, variations in volume of the pressure detection chamber can be decreased in comparison with a conventional method by caulking, resulting in decreased variations in output.